The present invention relates to a process for manufacturing a mold from the shapes of a piece which it is desired to obtain by molding.
It relates more particularly to the manufacture of a mold formed from at least two parts movable in translation with respect to each other along a given axis, and each having a part of the impression of the piece to be molded.
Thus, in the closed position of the mold, these two parts are assembled jointingly together and define by their impressions, a closed volume having substantially the dimensions of the piece and in which the molding material may be injected. Once the material has set, the molded piece is removed from the mold by separating the two parts of the mold by a movement during which the piece which has just been molded is extracted from at least one of the mold parts, the piece then being freed from the other part for example by means of an ejector.
It is clear that in the case of a piece having a prismatic shape, removal from the mold may take place without difficulty. On the other hand, in the case of pieces having more complex shapes, it is necessary to design molds in which the joint planes of the two mold parts are particularly designed so as to allow removal from the mold without having to use, as much as possible, drawers or other expedients which considerably increase the complexity of the mold and consequently its cost price.
Of course, to this problem of determining the joint planes are added numerous other problems which should be resolved such for example as the problem of shrinkage, the problems of draw tapers, of undercuts etc. . .
In the present state of the technique, for determining the structure and shapes of the mold, the mold pattern designer uses at the outset drawings of the piece in two dimensions. He reproduces these drawings with new dimensions taking into account the shrinkage of the piece during molding.
After studying the shapes of the piece, he then makes an approximate search for the joint planes of the two parts of the mold.
This is a particularly delicate operation requiring all the experience and all the knowledge of the mold pattern designer for finding the best possible solution considering the specifications.
The designer must then define the piece in position in space with respect to the impressions, then represent the piece in perspective so as to obtain visualization thereof in three dimensions.
He must further represent the negative of the pieces in three dimensions (or simply make tracings of the solid and hollow parts of the piece). This representation must in particular comprise exploded views of the fixed and mobile parts of the mold and definition of all the shapes of the impressions.
In a subsequent phase, the mold pattern designer cuts out the impression portions then procedes with finishing the design and possibly optimization thereof.
It can therefore be seen that the whole of the work to be carried out for defining a mold by using this method is relatively long and costly. This method further requires the employment of particularly competent and experienced pattern mold designers capable of defining the best possible joint planes from two-dimensional drawings.